South Korea's unification ministry on Thursday voiced strong regret over North Korea's claim that its COVID-19 outbreak had originated from the South and its threats of an unspecified retaliatory step.

Earlier in the day, Pyongyang's state media reported that leader Kim Jong-un held a national meeting the previous day and declared victory in the campaign against COVID-19.

During the session, his younger sister Kim Yo-jong, who serves as vice department director of the Central Committee of the Workers' Party of Korea, reiterated Pyongyang's assertion that "alien things" from the South carried the virus into the North and raised the need to take "deadly retaliatory" countermeasures.

The government "expresses strong regret over North Korea's insolent and threatening remarks based on repeated groundless claims regarding the inflow of the coronavirus at the national meeting on reviewing anti-epidemic measures," an official at the ministry told reporters on the customary condition of anonymity.

The South's Joint Chiefs of Staff said that it is maintaining a "firm" readiness posture and preparing against "various possibilities."

Last month, the North claimed its coronavirus outbreak originated from alien things found near the inter-Korean border, alluding to balloon-carried materials sent by North Korean defector groups in South Korea, such as anti-Pyongyang leaflets. (Yonhap)